The matrix proteins of bones and teeth play key roles in the structure and functions of these tissues. Our objective was to study their function and regulation using a combination of in vitro and in vivo analysis. The genes we have focused on are biglcyan (BGN) and bone sialoprotein (BSP) both of which are highly expressed in bones and teeth. A major challenge for the study of human gene function and regulation in vitro is the extreme inefficiency of DNA transfer DNA into human non-transformed cultured cells. In order to devise new methods to overcome this blockade we tested two adenoviral based procedures using marrow stromal fibroblasts and trabecular bone cells both derived from human skeletal material. Adenoviruses containing b-galactosidase recombinant genes showed substantial gene transfer (10,000X over control) indicating that adenovirus based methods are ideal for these unique cell types. We also tested adenoviruses modified with poly-lysine additionally and found they transferred genes into mulitlayer highly differentiated non-dividing cells also with high efficiency; this latter procedure has numerous advantages in that it is rapid, simple, and does not require incorporation of transgenes into the viral genome. To examine the function of matrix proteins in vivo we generated bgn-deficient mice. While apparently normal at birth, these mice display a phenotype characterized by reduced growth and bone mass due to the absence of bgn. To our knowledge, this is the first report that deficiency of a non-collagenous extracellular matrix protein (ECM) that leads to a skeletal phenotype that is marked by low bone mass which becomes more obvious with age. These mice may serve as an animal model to study the role of ECM proteins in osteoporosis.